GUESS has relative values today, but GUESS isn't using relative values to rank all positions together, which is why we would see certain positions dominate rankings.
For letter grades by formation, it is my first attempt at it. I'm not married to it. It is not simple to get this right. Might not even be possible to get it right. Some background...
I fill out a formation by picking top rated players for each position role rating. So one thing you will notice is that a team who doesn't have enough players to fill a certain position will have a lower letter grade, likely a C/D/F grade (e.g. if you only have 2 WR's = poor letter grade for Shotgun).
For the actual calculation, my concept is similar to how GUESS does it but not identical. Each formation has a total of 22 "points" to distribute across the 11 positions. I won't go into the full detail for every formation, but here is the general concept using Pro Set as an example.
Pro Set Running - RB's would be weighted the highest
QB - take best QB Run role rating
RB1 - take the best overall RB role rating
RB2 - take the next best RB with highest FB role rating
WR1 - take best WR rating
WR2 - take next best WR rating
TE - take the best TE Blocking role rating
OL - take the top 5 OL Run role rating
SUM the weighted ratings and then calculate relative value against all other schools for Pro Set Running.
Pro Set Passing - QB would be weighted the highest
QB - take the best QB passing role rating
RB1 - take the best RB possession role rating
RB2 - take the next best RB possession role rating
WR1 - take the best WR possession role rating
WR2 - take the next best WR possession role rating
TE - take the best TE possession role rating
OL - take the top 5 OL Pass role ratings
SUM the weighted ratings and then calculate relative value against all other schools for Pro Set Passing.